Oklahoma prison officials put a halt to the execution of an inmate after botching the delivery of a new three-drug lethal injection cocktail, officials said.

Robert Patton, the director of the Oklahoma Department of Corrections, halted Clayton Lockett’s execution about 20 minutes after the first drug was administered.

A news reporter for NBC station KFOR in Oklahoma City who witnessed the execution said that an intravenous line into Lockett’s arm blew out.

Patton earlier said there was a vein failure, but later confirmed a line blew during the planned execution.

Lockett suffered a massive heart attack and died at 7:06 p.m. CT, Patton confirmed.